This invention relates to an electronic control circuit for blowers in vehicles. The present invention is concerned particularly with a direct current analogue control circuit for a blower motor in a vehicle and which has particular utility in compensating for dynamic pressure effects.
Blowers are required for heating and cooling interiors of vehicles and also for air conditioning installations. It is important for the constant inside temperature that the blower air volume remains constant, regardless of speed of the vehicle and the like. In general, blowers with blades bent forward are used, since these blowers have a correspondingly steep characteristic curve and operate in the normal range with a relatively low rpm, i.e. they make little noise. It is disadvantageous that the amount of air supplied by the blower depends on the dynamic pressure which is in turn determined by the air inlet openings in the vehicle.
Control for D.C. blowers are known with compensating resistors which limit the voltage to the blower motor. In particular, air-cooled installations with fixed rotary or sliding resistors are known. Electronic fan rpm controls are also known, which make it possible to keep the voltage to the blower motor constant at a preset value and have electronic overload protection. The disadvantage is that with a constant voltage to the blower motor the rpm is kept constant, so that when the dynamic pressure increases, an increasing amount of air will be supplied, while the dynamic pressure exerts an additional rotational movement on the blower.